The official banner, produced by the United Nations Food and Agriculture Organization, to celebrate World Soil Day 2014. Photo: FAO
By Veronika Meduna veronika.meduna@radionz.co.nz
Even though soil is all around us, it is probably the most overlooked natural resource.
To build awareness of the importance of healthy soils, the United Nations Food and Agriculture Organization has declared the 5th of December as World Soil Day and the year 2015 as the International Year of Soils.
To mark World Soil Day, soil scientists have gathered in Hamilton this week for the Soil Science Society conference to discuss the latest research on soils and their relevance to food, fuel and fibre production and ecosystems services. They also headed into the field to explore different land uses and soil types, including the volcanic soils of the central North Island.
In the soil pit: Waikato University geoscientist David Lowe leads a field excursion to explore the layered deposits from the Taupo eruption. Photo: RNZ / Veronika Meduna
About 15 per cent of the North Island is covered in silica-rich pumice soils, which were long thought of as “undesirable” because of their low fertility and susceptibility to drought and erosion. But for Waikato University geoscientist David Lowe, who led a fieldtrip across the Taupo Volcanic Zone, pumice soils have gone from despised to highly desirable.
'Pumice soils … are very weakly weathered, very infertile and quite difficult to farm. After the First World War, a lot of the returned servicemen were sold or given cheapish blocks of land to pay off, but they found the big problem was that the cattle and sheep never thrived. The grass was growing but the cattle and sheep had a strange wasting disease which they called bush sickness.' _ David Lowe
It was clear that the wasting of livestock had something to do with the quality of the soil, but it took another 20 years to work out that the problem was a deficiency in the trace element cobalt.
By that stage, the Great Depression had hit and many farmers were forced to walk off the land. Instead, pine trees were planted – and they thrived. “Out of the adversity of these pumice soils came a new plantation forestry industry,” says David Lowe.
Soils are classified into orders, groups, subgroups and families. This map displays New Zealand’s soil orders. Photo: Waikato Regional Council
Now, some of the pine forests are being converted back to dairy farms, and Waikato University soil scientist Louis Schipper says it is important to monitor the effects such changes in landuse have on soil properties. "When you’ve got pine trees, they are just taking the nutrients from the soil as it stands, they put on wood and over 25 years they accumulate enough to able to be harvested. When you go to a landuse like pasture, it’s going to be a lot more intensive. There’s a constant removal of nutrients and products … that need to be replaced. So you now need to manage that soil more rapidly and have to even respond on a seasonal basis.”
He says New Zealand is a special place for soil studies because of our relatively short history of human impacts.
'If you think about New Zealand, 800 years ago there were no people and we had a completely different soil than what we have now. You wouldn’t recognise it.' _ Louis Schipper
People have fundamentally altered the properties of soil, he says, and his research focus is both fundamental and pragmatic. “Watching the changes in the amount of carbon in soils is important because that’s one avenue we have for looking at decreasing CO2 concentrations in the atmosphere.”
In another type of landuse, the Taupo District Council is using pumice soils to dispose of wastewater. In the past, treated wastewater was simply discharged into the Waikato River, but in 1995, the council decided to use land treatment to reduce the nutrient load of wastewater and to remove microbes. “Eighty to 90 on the nitrogen applied is removed in the crop, which is mostly ryegrass,” says Nicole Hancock. The grass is harvested and haylage bales sold as animal feed.
Soil is the Earth’s skin. It provides the link between biology and geology, and the process of weathering can take a hundred to a thousand years to produce one centimetre of soil. In its effort to raise awareness of the importance of healthy soils, the UN has set up the Global Soil Partnership, and Our Changing World has featured the launch of the Pacific sector of this initiative.
Listen below to join soil scientists as they explore the North Island's volcanic soils.
